IOSI-02 continuous Iron-Ratio output

For in-line redox state monitoring of the glass melt, the standard analog and digital outputs of the IOSI-02 oxygen sensor interface include glass melt temperature (T), oxygen cell millivolt signal (EMF), and the partial oxygen pressure of the melt (log pO₂). However, instead of log pO₂, furnace operators may prefer to use the continuous Iron-Ratio (IR) of the cold glass as the IOSI output parameter.

The log pO₂ of the glass melt is considered a scientific parameter, which may not be intuitive for daily plant operations. In the container glass industry, operators typically express the redox state using the iron-ratio of the cold glass product, determined through daily off-line laboratory analysis of a sample taken from the conveyor belt and measured via spectroscopy. Providing the same parameter, the iron-ratio, as a continuous sensor output enhances clarity, improves operational relevance, and helps prevent miscommunication between furnace operators and laboratory personnel regarding redox set-points and process control window.

The graph below illustrates the continuous iron-ratio measured by a redox sensor installed in the feeder channel of a furnace producing emerald green container glass. Following calibration of the IOSI-02 using iron-ratio values obtained from laboratory spectroscopic analysis, the real-time iron-ratio output can be activated. The data shows that the sensor’s measurements align closely with the daily laboratory results, even without recalibration of the IOSI-02 since the initial setup.

The benefit of an in-line redox sensor becomes immediately apparent: while the laboratory iron-ratio is typically available only once every 24 hours as a single data point, the continuous sensor output provides real-time insights into the iron-ratio value, the direction of shift (toward reduction or oxidation) and it’s rate of change throughout the day!

online iron ratio 984x529

Practical implementation

A standard IOSI-02 unit (configured with log pO₂ on I-out3) can be easily reconfigured as an IOSI-02-IR (outputting iron-ratio on I-out3) by uploading the dedicated IOSI-02-IR calculation program via the USB port, using the IOSI02config PC application.

To enable long-distance serial communication over RS485 using the Modbus protocol, the IOSI-02-IR must be operated in conjunction with the IOSI02modbus PC application. This software allows users to read, graphically visualize, and store both measurement data and calculated values directly from the sensor.

Before initiating the online iron-ratio output, the IOSI-02-IR must be calibrated using the most recent laboratory-determined iron-ratio of the cold glass (denoted as IR₀). The IOSI02modbus PC application includes a dedicated calibration feature, known as Time-Delayed Calibration, which allows users to input the analyzed iron-ratio result from the lab.

From that point onward, the IOSI-02-IR provides a continuous iron-ratio output for the cold glass. This value is dynamically calculated based on changes in the oxygen cell EMF and temperature recorded since the initial calibration with the laboratory reference.

Time Delayed Calibration procedure

Since the laboratory iron-ratio result is typically available several hours after the corresponding glass melt has passed the sensor, the IOSI02modbus PC application includes a specialized calibration feature known as Time-Delayed Calibration (TDC).

A schematic illustration of the continuous IR output and the calibration process is shown in the figure on the right. In this diagram, t₀ represents the time when the glass melt passed the sensor, and t_cal indicates the time at which the calibration is performed.

The TDC procedure in the IOSI02modbus app is designed for ease of use: simply click on the graph at t₀, press the TDC button, and enter the laboratory iron-ratio result (IR₀) in the pop-up window that appears.